The present invention relates generally to an improved method of manufacturing a composite material. More specifically, the present invention relates to a method of manufacturing a molded material, formed from a base matrix loaded with filler material, that results in a completed composition having a uniformly colored appearance.
In the prior art, it is known to load base polymer matrix materials with thermally conductive filler materials to create a composition that, after molding, has thermally conductive properties. In addition, it is also known for the base matrix molding material to take on to a large extent, the color of the filler material that is loaded therein. Since the concentration of the filler material within the composition may approach 60% or more by volume, the color of the filler can have a significant impact on the color of the final composition. An example of such a composition is a polymer base matrix with carbon fiber filler loaded therein. The polymer base matrix allows the material to be easily injection molded, while the carbon fiber improves the overall thermal conductivity of the molded part. As a result, the molded part has high thermally conductive properties and is also net shape molded, meaning that the part is in its final configuration obviating the need for further machining.
The drawback in the present technology however, is that while the finished product""s resultant color is influenced by the color of the filler material loaded therein, the overall color is not uniform throughout the part. This uneven coloring results from the fact that the base and filler components used in the process respectively have two different colors. When mixed, as is well known in the art, the two components each contribute to the final appearance of the molded part and often cause a marbled, uneven or erratic appearance that results in an unattractive part. In addition, typically the final color is simply not the correct or desired color for the intended use of the molded part. Using the example above, the resulting color of a molded part, formed from a base matrix polymer with a light color and carbon fiber filler with a dark gray color, would be mottled and streaky with veins of dark gray randomly distributed throughout the part. Further, even coloration may also be functionally critical. For example, an even black color may be required for a satellite dish to ensure absorption of a certain wavelength of radiation.
Since these molded composite materials are often used to form parts that are employed in the construction of an article that can be seen, it is important to have a method by which these parts can be fabricated that results in an aesthetically attractive appearance. For example, a thermally conductive composite material may be employed to construct the outer case of a laptop computer. The material would impart a highly desirable characteristic to the computer case by allowing it to efficiently conduct and dissipate heat that is generated within the computer, however, if fabricated using the current technology, the computer would have an undesirable, uneven and streaky appearance.
In view of the foregoing, there is a demand for a moldable composite material that has a uniformly colored appearance and is highly thermally conductive. In addition, there is a demand for a thermally conductive composite material that can be molded or cast into complex product geometries with a resulting uniformly colored appearance.
The present invention preserves the advantages of prior art thermally conductive plastic compositions, namely net shape moldablity and thermal conductivity. In addition, it provides new advantages of uniform coloration not found in currently available compositions.
The present invention is generally directed to a novel and unique process for molding a thermally conductive plastic composite material with a uniform and even color. The present invention provides a process that has application in producing products where the use of a thermally conductive polymer is indicated and the aesthetic appearance of the final part is important. This process provides for net shape moldable, thermally conductive parts that can be fabricated in the color desired by the end user and can be produced with a uniform appearance.
The process of the present invention provides for the filler material to be colored to match as closely as possible the desired color of the end product before mixing it into a base polymer matrix. The mixture is then molded into the desired final shape. The resulting composition has an even uniform color that is suitable for use in highly visible applications for example, computer and cell phone cases or satellite dish receivers. In these applications there is a need to quickly dissipate heat to the exterior of the device. The polymer case of these devices would be the ideal surface through which to accomplish this heat dissipation function, but prior to the present invention this was infeasible. Although the technology existed to mold thermally conductive polymers, the end product did not have a sufficiently uniform appearance to be used in the fabrication of external component parts.
The present invention requires that, prior to the mixing and molding steps, the filler material be colored with a coating material that is the desired color of the finished product. The particular coloring process in accordance with the present invention depends on the filler to be employed. In products where the thermally conductive filler is a metallic flake material, the coloring process would be either spraying or anodizing. For example, if aluminum flakes are used as filler, the flakes are first anodized in a color that closely matches the desired end color of the product and then mixed into the base polymer matrix and finally subjected to a conventional molding process. If the thermally conductive filler used is of a non-metallic type, like carbon fiber, the fibers would be dyed to match the desired resulting color and then mixed into the base polymer and molded into the desired shape.
The present invention has potential impact not only in the production of composite components that have a color that is suitable for aesthetic appearances, but will also allow the components to be colored in a manner that will best stabilize them against the elements to which the part may be subjected. For example, a thermally conductive composite could be employed to fabricate the casing and dish for a satellite receiver. A device of this type, by its nature must be installed in an environment where it is constantly subjected to damaging sunlight that will potentially breakdown the composite material. For example, the color black may be preferred, a coloration that could not be achieved in a prior art thermally conductive composition. Prior to the present invention the color of the composite was limited to a color that was consistent with the color of the filler material and base polymer matrix. Using the present invention, a composite can be fabricated in a color that is best suited to reflect and withstand the exposure to sunlight.
It is therefore an object of the present invention to provide a process by which a thermally conductive composite material can be colored uniformly.
It is an object of the present invention to provide a process where a conductive composite material has a uniform appearance after molding.
Another object of the present invention is to provide a conductive composite material that enables the molding of complex part geometries with a uniform color throughout the part.
It is yet a further object of the present invention to provide a conductive composite material that can be fabricated in a color desired by the end user of the component.
It is another object of the present invention to provide a thermally conductive composite that can be fabricated of a uniform color so as to withstand prolonged exposure to sunlight.